title: A CLCN1 mutation in dominant myotonia congenita impairs the increment of chloride conductance during repetitive depolarization.
abstract: Myotonia congenita is caused by mutation of the CLCN1 gene, which encodes the human skeletal muscle chloride channel (ClC-1). The ClC-1 protein is a dimer comprised of two identical subunits each incorporating its own separate pore. However, the precise pathophysiological mechanism underlying the abnormal ClC-1 channel gating in some mutants is not fully understood. We characterized a ClC-1 mutation, Pro-480-Thr (P480T) identified in dominant myotonia congenita, by using whole-cell recording. P480T ClC-1 revealed significantly slowed activation kinetics and a slight depolarizing shift in the voltage-dependence of the channel gating. Wild-type/mutant heterodimers exhibited similar kinetic properties and voltage-dependency to mutant homodimers. Simulating myotonic discharge with the voltage clamp protocol of a 50 Hz train pulse, the increment of chloride conductance was impaired in both wild-type/mutant heterodimers and mutant homodimers, clearly indicating a dominant-negative effect. Our data showed that slow activation gating of P480T ClC-1 impaired the increment of chloride conductance during repetitive depolarization, thereby accentuating the chloride conductance reduction caused by a slight depolarizing shift in the voltage-dependence of the channel gating. This pathophysiology may explain the clinical features of myotonia congenita.
authors.affiliation: First Department of Internal Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki 852-8501, Japan. akrtjn@nagasaki-u.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Tsujino
authors.forename: Muneshige
authors.initials: M
authors.lastname: Kaibara
authors.forename: Hideki
authors.initials: H
authors.lastname: Hayashi
authors.forename: Hiroto
authors.initials: H
authors.lastname: Eguchi
authors.forename: Susumu
authors.initials: S
authors.lastname: Nakayama
authors.forename: Katsuya
authors.initials: K
authors.lastname: Sato
authors.forename: Taku
authors.initials: T
authors.lastname: Fukuda
authors.forename: Yohei
authors.initials: Y
authors.lastname: Tateishi
authors.forename: Susumu
authors.initials: S
authors.lastname: Shirabe
authors.forename: Kohtaro
authors.initials: K
authors.lastname: Taniyama
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kawakami
mesh_terms: D000368:Aged; D000595:Amino Acid Sequence; D018118:Chloride Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009224:Myotonia Congenita / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D017433:Protein Structure, Secondary
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels